This invention relates to an improved process for preparing modified polymers having a low degree of unsaturation. Particularly it relates to a catalytic process for carrying out such reactions, more particularly to the use of a metal-containing catalyst, especially catalysts of specific metal salts of weak acids.
Modified polymers of the type of interest herein, specifically rubbery polymers, are described in U.S. Pat. No. 3,915,907 and U.S. Pat. 3,970,133 (R. J. Hopper) incorporated herein by reference. The desirability and advantages of such polymers was additionally disclosed in articles authored and co-authored by R. J. Hopper (Rubber Chemistry and Technology, Vol. 49, p. 341-352 (1976) and International Conference on Advances in the Stabilization and Controlled Degradation of Polymers, Lucerne, Switzerland, May 23-25, 1984), also incorporated herein by reference.
These references describe the reaction of various N-chlorothioamides, and particularly N-chlorothio-sulfonamides with various ethylene propylene diene monomer (EPDM) rubbers in solution (see, e.g., Examples I-XII of U.S. 3,915,907) as well as by mixing in a Banbury.RTM. type internal mixer (Examples XIII-XVI of U.S. 3,915,907). Furthermore, in Example XVII of the same reference, there is disclosed in a solution reaction the use of powdered anhydrous zinc chloride (this is referred to as a catalyst in Table I, footnote g and page 346 of the cited Rubber Chemistry and Technology article). The references contain no further disclosure concerning the effect of zinc chloride nor do they suggest the use of other catalytic agents. Prior to the invention herein, the melt phase graft reaction had not been achieved under commercially useful conditions (i.e., rate, conversion and product quality). It is the discovery of selective catalysts that has permitted this advance.
Mixtures or blends of low-unsaturation rubbery polymers, particularly EPDM, with highly unsaturated rubbery polymers are of practical importance because of the superior ozone resistance imparted to the blend by the low-unsaturation EPDM rubber. Unfortunately, the presence of the low-unsaturation rubber also affects the mechanical and hysteresis characteristics of the vulcanizates in an adverse manner, as evidenced by lower tensile strength and modulus values, and by higher dynamic heat build-up and permanent set. These undesirable responses are contributed to by the mutual incompatibility of the two types of rubber, the substantially slower cure rate of the low-unsaturation rubber, and the greater affinity of the typically polar curatives for the high-unsaturation rubber. As a result, the vulcanized blend is a heterogeneous dispersion of poorly cured and/or largely uncured low-unsaturation rubber in well cured high-unsaturation rubber. The resulting poorer mechanical and hysteresis properties severely limit, or preclude, the use of such blends in articles subjected to severe service requirements such as tires. A method for improving the physical and dynamic properties of such rubbery polymer vulcanized blends is of considerable commercial and practical importance.